/Engine/Source/Editor/UnrealEd/Public/LevelEditorViewport.h
The actors that are currently being placed in the viewport via dragging
static [TArray](API\Runtime\Core\Containers\TArray)< [TWeakObjectPtr](API\Runtime\Core\UObject\TWeakObjectPtr)< [AActor](API\Runtime\Engine\GameFramework\AActor) > > DropPreviewActors;